桌子如何调节面对面个体之间的空气传播风险
How a table modulates the risk of airborne transmission between facing individuals
AI总结：
本研究利用高保真大涡模拟分析面对面围桌场景，揭示桌—排放源距离如何改变呼出气流与颗粒输运，并阐明桌子对短距离空气传播和污染物传播风险的调节作用。
摘要：
空气传播已被认为是SARS-CoV-2（导致COVID-19大流行的病毒）的重要传播途径。虽然咳嗽和打喷嚏是产生受感染气溶胶的显著来源，并伴随影响范围较远的气流，但无症状传播的普遍性凸显了社交活动的重要性。围坐在桌子旁是一种常见的人类互动场景，它不仅固定了静态交谈者之间的典型距离，还通过同时充当气流转向装置和液滴沉积表面来影响空气传播。在这里，我们使用高保真大涡模拟来刻画两人在一张典型桌子旁面对面时的短距离空气传播。我们表明，与自由浮力气团和射流自然传播的距离相比，桌子与排放源之间的距离构成了一个新的长度尺度，会改变鼻呼吸、说话和大笑时常见的向下呼出气流。当桌子靠近排放者时，其主要作用是限制所排放颗粒的向前扩散。然而，如果个体之间的距离过短，到达接收者的颗粒会变得更加集中，从而增加传播风险。此外，对大笑等用力呼气的模拟表明，桌子起到过滤器的作用，会收集那些原本会留在自由射流中的中等尺寸颗粒，但在这种情况下，这些颗粒可能参与污染物传播途径。桌子引入了一个取决于呼出物质惯性的颗粒截断尺寸，从而改变了悬浮在空气中的颗粒尺寸分布。
英文摘要：
Airborne transmission has been recognized as an important route of transmission for SARS-CoV-2, the virus responsible for the COVID-19 pandemic. While coughing and sneezing are spectacular sources of production of infected aerosols with far-reaching airflows, the prevalence of asymptomatic transmissions highlighted the importance of social activities. Gathering around a table, a common scenario of human interactions, not only fixes a typical distance between static interlocutors, but influences airborne transmission, by serving both as a flow diverter and a surface for droplet deposition. Here, we use high-fidelity large-eddy simulations to characterize short-range airborne transmission when two people face each other at a typical table. We show that compared to the natural distance travelled by free buoyant puffs and jets, the distance between the table and the emission constitutes a new length scale that modifies downward exhaled flows, common during nose breathing, speech, and laughter. When the table is close to the emitter, its main effect is to restrict the forward spread of emitted particles. However, if the distance between individuals is too short, particles reaching the recipient become more concentrated, rising transmission risks. Additionally, simulations of forceful exhalations, like laughter, demonstrate that the table acts as a filter that collects medium-sized particles that would have remained in the free jet otherwise, but can in that case be involved in the fomite transmission route. The table introduces a cut-off size for particles that depends on the inertia of the exhaled material, thereby modifying the size distribution of particles suspended in the air.
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